测试导航

在发布应用之前测试应用的导航逻辑非常重要，以便验证您的应用按预期工作。

导航组件负责管理目标之间的导航、传递参数以及与FragmentManager协作的所有工作。这些功能已经过严格测试，因此无需在您的应用中再次测试它们。但是，需要测试的是片段中应用特定代码及其NavController之间的交互。本指南介绍了一些常见的导航场景以及如何测试它们。

测试片段导航

要单独测试片段与其NavController的交互，Navigation 2.3 及更高版本提供了一个TestNavHostController，它提供用于设置当前目标并在NavController.navigate()操作后验证回退堆栈的 API。

您可以通过在应用模块的build.gradle文件中添加以下依赖项，将导航测试构件添加到您的项目中

Groovy

dependencies {
  def nav_version = "2.8.4"

  androidTestImplementation "androidx.navigation:navigation-testing:$nav_version"
}

Kotlin

dependencies {
  val nav_version = "2.8.4"

  androidTestImplementation("androidx.navigation:navigation-testing:$nav_version")
}

假设您正在构建一个琐事游戏。游戏从标题屏幕开始，当用户点击播放时导航到游戏内屏幕。

表示标题屏幕的片段可能如下所示

Kotlin

class TitleScreen : Fragment() {
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ) = inflater.inflate(R.layout.fragment_title_screen, container, false)

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        view.findViewById<Button>(R.id.play_btn).setOnClickListener {
            view.findNavController().navigate(R.id.action_title_screen_to_in_game)
        }
    }
}

Java

public class TitleScreen extends Fragment {

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater,
            @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_title_screen, container, false);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        view.findViewById(R.id.play_btn).setOnClickListener(v -> {
            Navigation.findNavController(view).navigate(R.id.action_title_screen_to_in_game);
        });
    }
}

为了测试当用户点击播放时应用是否正确地将用户导航到游戏内屏幕，您的测试需要验证此片段是否正确地将NavController移动到R.id.in_game屏幕。

结合使用FragmentScenario、Espresso和TestNavHostController，您可以重新创建测试此场景所需的条件，如下例所示

Kotlin

@RunWith(AndroidJUnit4::class)
class TitleScreenTest {

    @Test
    fun testNavigationToInGameScreen() {
        // Create a TestNavHostController
        val navController = TestNavHostController(
            ApplicationProvider.getApplicationContext())

        // Create a graphical FragmentScenario for the TitleScreen
        val titleScenario = launchFragmentInContainer<TitleScreen>()

        titleScenario.onFragment { fragment ->
            // Set the graph on the TestNavHostController
            navController.setGraph(R.navigation.trivia)

            // Make the NavController available via the findNavController() APIs
            Navigation.setViewNavController(fragment.requireView(), navController)
        }

        // Verify that performing a click changes the NavController’s state
        onView(ViewMatchers.withId(R.id.play_btn)).perform(ViewActions.click())
        assertThat(navController.currentDestination?.id).isEqualTo(R.id.in_game)
    }
}

Java

@RunWith(AndroidJUnit4.class)
public class TitleScreenTestJava {

    @Test
    public void testNavigationToInGameScreen() {

        // Create a TestNavHostController
        TestNavHostController navController = new TestNavHostController(
            ApplicationProvider.getApplicationContext());

        // Create a graphical FragmentScenario for the TitleScreen
        FragmentScenario<TitleScreen> titleScenario = FragmentScenario.launchInContainer(TitleScreen.class);

        titleScenario.onFragment(fragment ->
                // Set the graph on the TestNavHostController
                navController.setGraph(R.navigation.trivia);

                // Make the NavController available via the findNavController() APIs
                Navigation.setViewNavController(fragment.requireView(), navController)
        );

        // Verify that performing a click changes the NavController’s state
        onView(ViewMatchers.withId(R.id.play_btn)).perform(ViewActions.click());
        assertThat(navController.currentDestination.id).isEqualTo(R.id.in_game);
    }
}

上面的示例创建TestNavHostController的实例并将其分配给片段。然后，它使用 Espresso 来驱动 UI 并验证是否采取了适当的导航操作。

与真实的NavController一样，您必须调用setGraph来初始化TestNavHostController。在此示例中，被测试的片段是我们图表的起始目标。TestNavHostController提供了一个setCurrentDestination方法，允许您设置当前目标（以及可选地该目标的参数），以便NavController在测试开始之前处于正确状态。

与NavHostFragment将使用的NavHostController实例不同，当您调用navigate()时，TestNavHostController不会触发底层的navigate()行为（例如FragmentNavigator执行的FragmentTransaction），它只会更新TestNavHostController的状态。

使用 FragmentScenario 测试 NavigationUI

在之前的示例中，提供给titleScenario.onFragment()的回调函数在片段的生命周期移动到RESUMED状态后被调用。此时，片段的视图已经创建并附加，因此在生命周期中可能为时已晚而无法进行正确的测试。例如，当在片段中使用带有视图的NavigationUI时，例如由片段控制的Toolbar，您可以在片段达到RESUMED状态之前使用您的NavController调用设置方法。因此，您需要一种方法在更早的生命周期阶段设置您的TestNavHostController。

拥有自身Toolbar的片段可以按如下方式编写：

Kotlin

class TitleScreen : Fragment(R.layout.fragment_title_screen) {
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        val navController = view.findNavController()
        view.findViewById<Toolbar>(R.id.toolbar).setupWithNavController(navController)
    }
}

Java

public class TitleScreen extends Fragment {
    public TitleScreen() {
        super(R.layout.fragment_title_screen);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        NavController navController = Navigation.findNavController(view);
        view.findViewById(R.id.toolbar).setupWithNavController(navController);
    }
}

这里我们需要在调用onViewCreated()时创建NavController。使用之前onFragment()的方法会在生命周期过晚设置我们的TestNavHostController，导致findNavController()调用失败。

FragmentScenario提供了一个FragmentFactory接口，可用于注册生命周期事件的回调函数。这可以与Fragment.getViewLifecycleOwnerLiveData()结合使用，以接收紧跟在onCreateView()之后的回调函数，如下例所示：

Kotlin

val scenario = launchFragmentInContainer {
    TitleScreen().also { fragment ->

        // In addition to returning a new instance of our Fragment,
        // get a callback whenever the fragment’s view is created
        // or destroyed so that we can set the NavController
        fragment.viewLifecycleOwnerLiveData.observeForever { viewLifecycleOwner ->
            if (viewLifecycleOwner != null) {
                // The fragment’s view has just been created
                navController.setGraph(R.navigation.trivia)
                Navigation.setViewNavController(fragment.requireView(), navController)
            }
        }
    }
}

Java

FragmentScenario<TitleScreen> scenario =
FragmentScenario.launchInContainer(
       TitleScreen.class, null, new FragmentFactory() {
    @NonNull
    @Override
    public Fragment instantiate(@NonNull ClassLoader classLoader,
            @NonNull String className,
            @Nullable Bundle args) {
        TitleScreen titleScreen = new TitleScreen();

        // In addition to returning a new instance of our fragment,
        // get a callback whenever the fragment’s view is created
        // or destroyed so that we can set the NavController
        titleScreen.getViewLifecycleOwnerLiveData().observeForever(new Observer<LifecycleOwner>() {
            @Override
            public void onChanged(LifecycleOwner viewLifecycleOwner) {

                // The fragment’s view has just been created
                if (viewLifecycleOwner != null) {
                    navController.setGraph(R.navigation.trivia);
                    Navigation.setViewNavController(titleScreen.requireView(), navController);
                }

            }
        });
        return titleScreen;
    }
});

使用此技术，NavController在调用onViewCreated()之前可用，允许片段使用NavigationUI方法而不会崩溃。

测试与返回堆栈条目的交互

当与返回堆栈条目交互时，TestNavHostController允许您通过它从NavHostController继承的API将控制器连接到您自己的测试LifecycleOwner、ViewModelStore和OnBackPressedDispatcher。

例如，在测试使用导航作用域ViewModel的片段时，必须在TestNavHostController上调用setViewModelStore

Kotlin

val navController = TestNavHostController(ApplicationProvider.getApplicationContext())

// This allows fragments to use by navGraphViewModels()
navController.setViewModelStore(ViewModelStore())

Java

TestNavHostController navController = new TestNavHostController(ApplicationProvider.getApplicationContext());

// This allows fragments to use new ViewModelProvider() with a NavBackStackEntry
navController.setViewModelStore(new ViewModelStore())